Metallurgical powder compositions and methods of making and using the same

ABSTRACT

The present invention provides iron-based metallurgical powder compositions and a method of making and using the same. The metallurgical powder compositions of the present invention contain certain amounts of an iron-alloy powder having iron and at least one alloying additive; substantially pure iron powder; and a carbon powder, such as graphite. The metallurgical powder compositions are prepared by admixing the iron-alloy powder with the iron powder and carbon powder. The metallurgical powder compositions thus produce and when formed into metal parts have, for example, improved machinability properties.

FIELD OF THE INVENTION

[0001] The present invention relates to improved iron-basedmetallurgical powder compositions and methods of making and using thesame. The iron-based powder compositions contain a mixture ofsubstantially pure iron powder and an iron-alloy powder that preferablycontains molybdenum as an alloying additive. The iron-based powdercompositions thus produced have improved machinability when formed intometal parts.

BACKGROUND OF THE INVENTION

[0002] Industrial usage of metal parts manufactured by the compactionand sintering of metal powder compositions is expanding rapidly into amultitude of areas. In the manufacture of such parts, metal powdercompositions are typically formed from metal-based powders and otheradditives such as lubricants, and binders. The metal-based powders aretypically iron powders that optionally may be alloyed with one or morealloying components.

[0003] A common technique for preparing an iron-alloy powder is to forma homogeneous molten metal composition containing iron and one or moredesired alloying components, and water atomizing the molten metalcomposition to form a homogeneous powder composition.

[0004] The metal-based powder, after any optional alloying, is oftenmixed with other additives to improve the properties of the final part.For example, the metal-based powder is often admixed with at least oneother alloying additive that is in powder form (“alloying powder”). Thealloying powder permits, for example, the attainment of higher strengthand other mechanical properties in the final sintered part.

[0005] The mixture of metal-based powder and optional alloying powdersare often also mixed with other additives such as lubricants and bindingagents to form the final metal powder composition. This metal powdercomposition is typically poured into a compaction die and compactedunder pressure (e.g., 5 to 70 tons per square inch (tsi)), and in somecircumstances at elevated temperatures, to form the compacted, or“green” part. The green part is then usually sintered to form a cohesivemetallic part and optionally finished. Examples of types of finishingsteps include machining the metal part (e.g., cutting, shaving,drilling, turning, milling, etc.) to the desired specifications.

[0006] One problem that occurs in the finishing of metal parts is thatthe metal parts are often difficult to machine. For example, a metalpart may be difficult to drill, leading to longer machining time,decrease in the life of the machine tool, and increased energy usage tooperate the machining equipment.

[0007] One solution to increasing the machinability of iron-based metalparts is disclosed in U.S. Pat. No. 4,018,632 to Schmidt(hereinafter“Schmidt”). Schmidt discloses that the machinability of an iron-basedmetal part can be improved through the use of a steel powder mixture ofgraphite and an iron-molybdenum-manganese alloy. The steel powder aftercompaction and sintering is heated and cooled according to certaintemperature profiles to improve the machinability of the metal part.

[0008] Another solution for increasing the machinability of iron-basedmetal parts is disclosed in U.S. Pat. No. 5,599,377 to Uenosono et al.(hereinafter “Uenosono”). Uenosono discloses a metal powder containing amixture of iron powder having less than 0.1 weight percent manganese andfrom about 0.08 weight percent to about 0.15 weight percent sulfur;graphite; and from about 0.05 to about 0.70 weight percent of at leastone compound selected from MoO₃ or WO₃. The iron powder is disclosed tohave excellent machinability and high strength due to the dissolution ofmolybdenum or tungsten compounds in the ferrite particles upon sinteringof the compacted metal part in a hydrogen-containing atmosphere.

[0009] Another solution proposed for improving the machinability ofmetal parts is disclosed in U.S. Pat. No. 5,679,909 to Kaneko et al.(hereinafter “Kaneko”). Kaneko discloses a sintered material having goodmachinability, where the sintered material is prepared by compacting andsintering a powder containing a mixture of composite oxide ofCaO—MgO—SiO₂ and an iron dominant metal matrix. The iron dominant metalmatrix may be prepared from a mixture of pure iron and “hard” particlesof FeMo, FeCr, FeW, or Tribaloy (containing Co—Ho—Cr and/or Co—Ho—Si).These hard particles are believed to contain at least 50 weight percentof the non-iron elements to provide the desired hardness.

[0010] Although the above compositions and/or methods provide ways ofimproving the machinability of a metal part, it would be desirable todevelop alternate compositions and methods. Preferably such alternatecompositions and methods would result in metal parts having comparableor improved machinability.

SUMMARY OF THE INVENTION

[0011] The present invention provides metallurgical powder compositionsand methods of making and using the same. The metallurgical powdercompositions, when formed into metal parts, exhibit improvedmachinability. This improved machinability is at least in part due tothe presence of certain amounts of at least one iron-alloy powder in themetallurgical powder compositions.

[0012] In one embodiment of the present invention, a method is providedthat includes providing an iron-alloy powder containing iron and atleast one alloying additive, where the alloying additive is present inan amount of from about 0.01 weight percent to about 7.0 weight percentand the iron is present in an amount of at least 85 weight percent basedon the total weight of the iron-alloy powder. Admixed with theiron-alloy powder is a substantially pure iron powder and carbon,typically a carbon powder, to form the metallurgical powder composition.The metallurgical powder composition preferably contains from about 5weight percent to about 40 weight percent of the iron-alloy powder, atleast 55 percent by weight of the iron powder, and at least 0.1 weightpercent carbon based on the total weight of the metallurgical powdercomposition.

[0013] In another embodiment of the present invention, a metallurgicalpowder composition is provided that contains from about 5 weight percentto about 40 weight percent of an iron-molybdenum alloy powder containingiron and molybdenum, where the amount of molybdenum is from about 0.10weight percent to about 7.0 weight percent and the amount of iron is atleast 85 weight percent based on the weight of the iron-molybdenum alloypowder. The metallurgical powder composition also contains at least 55weight percent of substantially pure iron powder, and from about 0.1weight percent to about 3.0 weight percent carbon.

[0014] The present invention also provides a method of forming a metalpart that includes providing a metallurgical powder composition of thepresent invention and compacting the metallurgical powder composition ata pressure of at least about 5 tsi to form a metal part.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a graph showing the mean thrust (in pounds) produced indrilling a metal part formed from an metallurgical powder composition ofthe present invention (Example 5) in comparison to metal parts made frommetallurgical powder compositions containing no iron-alloy powder(Comparative Examples 1 and 2).

DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention provides improved metallurgical powdercompositions that when formed into metal parts have improvedmachinability. By “machinability” it is meant the ability of a metalpart to be finished in some manner by machine operated tools. Forexample, metal parts produced in accordance with the methods of thepresent invention are preferably capable of being shaped, shaved,drilled, cut, turned, milled, or any combination thereof.

[0017] The metallurgical powder compositions of the present inventionare iron- based powder compositions containing substantially pure ironpowder, an iron-alloy powder, and carbon. These metallurgical powdercompositions may also optionally contain alloying powders, one or morelubricants, one or more binders, any other conventional powdermetallurgy additive, or any combination thereof.

[0018] It has been unexpectedly found that the machinability ofiron-based metal parts can be significantly improved through theaddition of certain amounts of iron-alloy powder in the metallurgicalpowder composition used to form the metal part. The iron-alloy powderuseful in the present invention is preferably made by partially orcompletely alloying iron with at least one alloying additive (forexample, molybdenum containing compounds) that can provide a hard phasefor improving machinability.

[0019] By “alloying” it is meant that the alloying additives and ironare admixed in a manner to permit melting, diffusion bonding or chemicalbonding of the iron and alloying additive. Suitable processes foralloying include for example “prealloying” and “diffusion bonding.”

[0020] Prealloyed and diffusion bonded iron-alloy powder may be madeaccording to any technique known to those skilled in the art. Forexample, prealloyed iron-alloy powder can be prepared from a melt ofiron and one or more desired alloying additives. Preferably, the melt isthen atomized so that the atomized droplets form a powder uponsolidification. Diffusion bonded iron-alloy powder can be prepared forexample by blending iron powder with one or more alloying additives,preferably in oxide form, and annealing the resulting mixture at hightemperatures (e.g., about 800 ° C. or greater). During annealing, thealloying compounds diffuse and partially alloy into the outer surfacesof the iron particles. A preferred diffusion bonding process isdisclosed in GB 1,162,702, which is hereby incorporated by reference inits entirety.

[0021] In a preferred embodiment of the present invention the iron-alloypowder is formed by a prealloying process. Prealloying has the advantageof facilitating complete alloying of the iron and alloying additives.

[0022] Preferably, the iron-alloy powder is present in the metallurgicalpowder composition at a concentration that is effective in improving themachinability of the metal part in comparison to a compositioncontaining no iron-alloy powder. Preferably, the amount of iron-alloypowder is from about 5 weight percent to about 40 weight percent, morepreferably from about 10 weight percent to about 30 weight percent, andmost preferably from about 12 weight percent to about 20 weight percent,based on the total weight of the metallurgical powder composition.

[0023] Iron that can be used to form the iron-alloy powder is preferablysubstantially pure iron containing not more than about 1.0% by weight,preferably no more than about 0.5% by weight, of normal impurities. Theiron may be in any physical form prior to prealloying. For example, theiron may be in powder form or in the form of scrap metal. For diffusionbonding, the iron is preferably in powder form.

[0024] Examples of suitable alloying additives for forming theiron-alloy powder include, but are not limited to elements, compounds,or alloys of molybdenum, manganese, magnesium, tungsten, chromium,silicon, copper, nickel, gold, vanadium, columbium (niobium), oraluminum, or oxides thereof; binary alloys of copper and tin orphosphorus; carbides of tungsten or silicon; silicon nitride; sulfidesof manganese or molybdenum, or combinations thereof. Preferably, theiron-alloy powder contains at least one alloying additive containingmolybdenum, manganese, magnesium, tungsten, chromium, silicon, copper,nickel, vanadium, oxides thereof, or any combination thereof, and morepreferably molybdenum, chromium, vanadium, tungsten, or combinationsthereof.

[0025] The total amount of alloying additive in the iron-alloy powderwill depend upon the alloying additive(s) chosen. Typically, thealloying additives are present in the iron-alloy powder in an amount offrom about 0.01 weight percent to about 7.0 weight percent, preferablyfrom about 0.10 weight percent to about 3.0 weight percent, and mostpreferably from about 0.10 weight percent to about 2.0 weight percent,based on the total weight of the iron-alloy powder.

[0026] The iron-alloy powder may also contain residual impurities, suchas from the iron used to form the iron-alloy powder. Generally, theiron-alloy powder contains minimum residual impurities of at least about0.15 weight percent and more preferably of at least about 0.25 weightpercent, and preferably contains maximum residual impurities of up toabout 1.0 weight percent, and more preferably up to about 0.9 weightpercent, based on the total weight of the iron-alloy powder.

[0027] The balance of the iron-alloy powder is preferably iron. Iron ispreferably present in the iron-alloy powder in an amount of at least85.0 weight percent, more preferably at least about 90.0 weight percent,and most preferably from about 94.0 weight percent to about 99.8 weightpercent.

[0028] In a preferred embodiment of the present invention, the iron isprealloyed with at least one alloying additive that contains molybdenumto form an iron-molybdenum prealloy powder. Molybdenum additive usefulin forming an iron-molybdenum prealloy powder is any element, compound,or alloy that contains molybdenum and is capable of alloying with ironin the prealloying process. The molybdenum additive may be, for example,an oxide of molybdenum such as molybdenum trioxide or a ferromolybdenumalloy. The molybdenum additive may also be substantially pure elementalmolybdenum (preferably having a purity of greater than about 90 wt %).Preferably, the molybdenum additive is an oxide of molybdenum such asmolybdenum trioxide.

[0029] In a most preferred embodiment of the present invention, theiron-molybdenum prealloy powder preferably contains from about 0.40weight percent to about 1.6 weight percent molybdenum, based on thetotal weight of the iron-molybdenum prealloy powder, and from about 97.4weight percent to about 99.50 weight percent iron. The iron-molybdenumprealloy powder preferably contains maximum residual impurities of about0.03 weight percent sulfur, about 0.02 weight percent silicon, and about0.01 weight percent nitrogen based on the total weight of the prealloypowder.

[0030] Examples of suitable iron-molybdenum prealloy powderscommercially available include Hoeganaes' ANCORSTEEL 150HP steel powder,85 HP steel powder, 50HP steel powder, or combinations thereof. Theamounts of molybdenum in the 150 HP, 85HP, and 50 HP steel powders arerespectively about 1.5 weight percent, 0.85 weight percent, and 0.55weight percent based on the total weight of the prealloy. Theseiron-molybdenum prealloy powders contain less than about 0.75 weightpercent of materials such as manganese, chromium, silicon, copper,nickel, or aluminum, and less than about 0.02 weight percent carbon,with the balance being substantially iron. Another example of acommercially available iron-molybdenum prealloy powder is Hoeganaes'ANCORSTEEL 4600V steel powder, which contains about 0.5-0.6 weightpercent molybdenum, about 1.5-2.0 weight percent nickel, about 0.1-0.25weight percent manganese, less than about 0.02 weight percent carbon,and the balance preferably being substantially iron. Other ANCORSTEELiron-molybdenum prealloy powders that are useful in the presentinvention include for example ANCORSTEEL 2000 and 737 steel powders. The150HP, 85HP, or 50HP steel powders are preferred for use as the prealloypowder in the present invention.

[0031] The metallurgical powder compositions of the present inventionalso contain substantially pure iron powder. Preferably, thesubstantially pure iron powder is present in the metallurgical powdercomposition in an amount of at least about 55 weight percent, morepreferably from about 60 weight percent to about 95 weight percent, andmost preferably from about 70 weight percent to about 90 weight percent,based on the total weight of the metallurgical powder composition.

[0032] Substantially pure iron powder that can be used in the inventionare powders of iron preferably containing not more than about 1.0% byweight, more preferably no more than about 0.5% by weight, of normalimpurities. Examples of such highly compressible, metallurgical-gradeiron powders are the ANCORSTEEL 1000 series of pure iron powders, e.g.1000, 1000B, and 1000C, available from Hoeganaes Corporation, Riverton,N.J. For example, ANCORSTEEL 1000 iron powder, has a typical screenprofile of about 22% by weight of the particles below a No. 325 sieve(U.S. series) and about 10% by weight of the particles larger than a No.100 sieve with the remainder between these two sizes (trace amountslarger than No. 60 sieve). The ANCORSTEEL 1000 powder has an apparentdensity of from about 2.85-3.00 g/cm³, typically 2.94 g/cm³.

[0033] The particles of iron-alloy powder and substantially pure ironpowder have a distribution of particle sizes. Typically, these powdersare such that at least about 90% by weight of the powder sample can passthrough a No. 45 sieve (U.S. series), and more preferably at least about90% by weight of the powder sample can pass through a No. 60 sieve.These powders typically have at least about 50% by weight of the powderpassing through a No. 70 sieve and retained above or larger than a No.400 sieve, more preferably at least about 50% by weight of the powderpassing through a No. 70 sieve and retained above or larger than a No.325 sieve. Also, these powders typically have at least about 5 weightpercent, more commonly at least about 10 weight percent, and generallyat least about 15 weight percent of the particles passing through a No.325 sieve. As such, these powders can have a weight average particlesize as small as one micron or below, or up to about 850-1,000 microns,but generally the particles will have a weight average particle size inthe range of about 10-500 microns. Preferred are iron-alloy particles orsubstantially pure iron particles having a maximum weight averageparticle size up to about 350 microns; more preferably the particleswill have a weight average particle size in the range of about 25-150microns, and most preferably 80-150 microns. Reference is made to MPIFStandard 05 for sieve analysis.

[0034] The metallurgical powder composition also preferably containscarbon. The carbon is preferably added as a substantially pure carbonpowder, such as graphite. Preferably, the carbon powder has a purity ofat least about 99.0 weight percent and more preferably a purity of atleast about 99.5 weight percent. The carbon powder may be in crystallineand/or amorphous form. Carbon is preferably present in the metallurgicalpowder composition in an amount of from about 0.1 weight percent toabout 3.0 weight percent, more preferably from about 0.2 weight percentto about 2.0 weight percent, and most preferably from about 0.3 weightpercent to about 1.2 weight percent, based on the weight of themetallurgical powder composition.

[0035] The metallurgical powder compositions of the present inventionmay also optionally contain alloying powders in addition to the carbonpowder. The term “alloying powder” as used herein refers to anyparticulate element, compound, or alloy powder physically blended withthe metallurgical powder composition, whether or not that additiveultimately alloys or partially alloys with the metallurgical powdercomposition.

[0036] Examples of optional alloying powders that may be present in themetallurgical powder composition include elements, compounds, or alloyscontaining molybdenum, manganese, copper, nickel, chromium, silicon,gold, vanadium, columbium (niobium), phosphorus, aluminum, boron, oroxides thereof; binary alloys of copper and tin, copper and nickel, orcopper and phosphorous; ferro-alloys of manganese, chromium, boron,phosphorus, or silicon; low melting ternary and quaternary eutectics ofcarbon in combination with elements selected from iron, vanadium,manganese, chromium, molybdenum or combinations thereof; carbides oftungsten or silicon; silicon nitride; aluminum oxide; and sulfides ofmanganese or molybdenum, and combinations thereof. Preferred alloyingpowders include elements, compounds, or alloys containing molybdenum,manganese, copper, nickel, chromium, vanadium, phosphorus, orcombinations thereof, and more preferably elements, compounds, or alloyscontaining copper, nickel, or combinations thereof.

[0037] The alloying powders are preferably present in the metallurgicalpowder composition in amounts of up to about 10 weight percent, andtypically in the range of from about 0.25 to about 10 weight percent,preferably from about 0.25 to about 7 weight percent, and morepreferably from about 0.5 to about 5 weight percent. The alloyingpowders generally have a weight average particle size below about 100microns, preferably below about 75 microns, more preferably below about30 microns, and most preferably in the range of about 5 microns to about20 microns. The particle size of the alloying powders is generallyrelatively small and can be analyzed by laser light scatteringtechnology as opposed to screening techniques. Laser light scatteringtechnology reports the particle size distribution in d_(x) values, whereit is said that “x” percent by volume of the powder has a diameter belowthe reported value. The alloying particles generally have a particlesize distribution such that they have a d₉₀ value of below about 100microns, preferably below about 75 microns, and more preferably belowabout 50 microns; and a d₅₀ value of below about 75 microns, preferablybelow about 50 microns, and more preferably below about 30 microns.

[0038] In a preferred embodiment of the present invention, themetallurgical powder composition contains an alloying powder containingcopper. The copper provides hardenability properties to metal partsformed from the metallurgical powder compositions. The copper containingpowder is preferably elemental copper having relatively few impurities.Preferably the copper containing powder contains at least 90 weightpercent, more preferably at least 98 weight percent, and most preferablyat least 99.5 weight percent copper based on the total weight of thecopper containing powder.

[0039] Preferably, the amount of copper containing powder present in themetallurgical powder composition of the present invention is such thatthere is at least 0.2 weight percent, more preferably from about fromabout 0.5 weight percent to about 4.0 weight percent, and mostpreferably from about 1.0 to about 3.0 weight percent elemental copper,based on the total weight of the metallurgical powder composition.

[0040] The metallurgical powder compositions of the present inventionmay also include any special-purpose additive commonly used withmetallurgical composition such as lubricants, machining agents, andplasticizers.

[0041] In a preferred embodiment of the present invention themetallurgical powder composition contains a lubricant to reduce theejection force required to remove a compacted part from the die cavity.Examples of typical powder metallurgy lubricants include the stearates,such as zinc stearate, lithium stearate, manganese stearate, or calciumstearate; synthetic waxes, such as ethylene bisstearamide orpolyolefins; or combinations thereof. The lubricant may also be apolyamide lubricant, such as PROMOLD-450, disclosed in U.S. Pat. No.5,368,630, particulate ethers disclosed in U.S. Pat. No. 5,498,276, toLuk, or a metal salt of a fatty acid disclosed in U.S. Pat. No.5,330,792 to Johnson et al., the disclosures of which are herebyincorporated by reference in their entireties. The lubricant may also bea combination of any of the aforementioned lubricants described above.

[0042] The lubricant is generally added in an amount of up to about 2.0weight percent, preferably from about 0.1 to about 1.5 weight percent,more preferably from about 0.1 to about 1.0 weight percent, and mostpreferably from about 0.2 to about 0.75 weight percent, of themetallurgical powder composition.

[0043] Preferred lubricants are ethylene bisstearamide, zinc stearate,Kenolube™ (supplied by Hoganas Corporation, located in Hoganas, Sweden),Ferrolube™ (supplied by Blanchford), and polyethylene wax. Preferably,these lubricants are added in an amount of from about 0.2 weight percentto about 1.5 weight percent based on the total weight of themetallurgical powder composition formed.

[0044] Other additives may also be present in the metallurgical powdercompositions, such as plasticizers and machining agents. Preferably,these other additives are present in the metallurgical powdercomposition in an amount of from about 0.05 weight percent to about 1.5weight percent, and more preferably from about 0.1 weight percent toabout 0.5 weight percent based on the total weight of the metallurgicalpowder composition. Plasticizers, such as polyethylene-polypropylenecopolymer, are typically used in connection with binders and/orlubricants. Machining agents, such as molybdenum sulfides, ironsulfides, boron nitride, boric acid, or combinations thereof aretypically used to aid in final machining operations. In a preferredembodiment, manganese sulfide is present in the metallurgical powdercomposition in an amount of from about 0.1 weight percent to about 0.75weight percent based on the weight of the metallurgical powdercomposition.

[0045] The metallurgical powder composition may also contain one or morebinding agents to bond the different components present in themetallurgical powder compostion so as to inhibit segregation. By “bond”as used herein, it is meant any physical or chemical method thatfacilitates adhesion of the components of the metallurgical powdercomposition.

[0046] In a preferred embodiment of the present invention, bonding iscarried out through the use of at least one binding agent. Bindingagents that can be used in the present invention are those commonlyemployed in the powder metallurgical arts. Examples of such bindingagents are found in U.S. Pat. No. 4,834,800 to Semel, U.S. Pat. No.4,483,905 to Engstrom, U.S. Pat. No. 5,154,881 to Rutz et al., and U.S.Pat. No. 5,298,055 to Semel et.al., the disclosures of which are herebyincorporated by reference in their entireties.

[0047] Such binding agents include, for example, polyglycols such aspolyethylene glycol or polypropylene glycol; glycerine; polyvinylalcohol; homopolymers or copolymers of vinyl acetate; cellulosic esteror ether resins; methacrylate polymers or copolymers; alkyd resins;polyurethane resins; polyester resins; or combinations thereof. Otherexamples of binding agents that are useful are the relatively highmolecular weight polyalkylene oxide-based compositions described in U.S.Pat. No. 5,298,055 to Semel et al. Useful binding agents also includethe dibasic organic acid, such as azelaic acid, and one or more polarcomponents such as polyethers (liquid or solid) and acrylic resins asdisclosed in U.S. Pat. No. 5,290,336 to Luk, which is incorporatedherein by reference in its entirety. The binding agents in the '336Patent to Luk can also advantageously act as lubricants. Additionaluseful binding agents include the cellulose ester resins, hydroxyalkylcellulose resins, and thermoplastic phenolic resins described inU.S. Pat. No. 5,368,630 to Luk, which is incorporated herein byreference in its entirety.

[0048] The binding agent can further be the low melting, solid polymersor waxes, e.g., a polymer or wax having a softening temperature of below200° C. (390° F.), such as polyesters, polyethylenes, epoxies,urethanes, paraffins, ethylene bisstearamides, and cotton seed waxes,and also polyolefins with weight average molecular weights below 3,000,and hydrogenated vegetable oils that are C₁₄₋₂₄ alkyl moietytriglycerides and derivatives thereof, including hydrogenatedderivatives, e.g. cottonseed oil, soybean oil, jojoba oil, and blendsthereof, as described in WO 99/20689, published Apr. 29, 1999, which ishereby incorporated by reference in its entirety herein. These bindingagents can be applied by the dry bonding techniques discussed in thatapplication and in the general amounts set forth above for bindingagents. Further binding agents that can be used in the present inventionare polyvinyl pyrrolidone as disclosed in U.S. Pat. No. 5,069,714, whichis incorporated herein in its entirety by reference, or tall oil esters.Preferred binding agents are polyethylene oxide and polyvinylacetate, orcombinations thereof, which are binding agents disclosed in WO 99/20689,

[0049] The amount of binding agent present in the metallurgical powdercomposition depends on such factors as the density, particle sizedistribution and amounts of the iron-alloy powder, the iron powder andoptional alloying powder in the metallurgical powder composition.Generally, the binding agent will be added in an amount of at leastabout 0.005 weight percent, more preferably from about 0.005 weightpercent to about 2 weight percent, and most preferably from about 0.05weight percent to about 1 weight percent, based on the total weight ofthe metallurgical powder composition.

[0050] In a preferred embodiment of the present invention, themetallurgical powder composition contains from about 10 weight percentto about 20 weight percent of an iron-molybdenum prealloy powder, fromabout 80 weight percent to about 90 weight percent substantially pureiron powder, from about 0.1 weight percent to about 1.2 weight percentcarbon that is preferably graphite powder, and from about 0.1 to about3.0 weight percent of copper that is preferably in the form of a coppercontaining powder. In this embodiment, the iron-molybdenum prealloypowder preferably contains from about 0.4 weight percent to about 2.0weight percent molybdenum and from about 98 weight percent to about 99.6weight percent iron. The percentages of iron, molybdenum, carbon andcopper in the metallurgical powder composition can be determined forexample by an elemental analysis.

[0051] The present invention also provides methods of preparingmetallurgical powder compositions. In the methods of the presentinvention, an iron-alloy powder that has preferably been prepared inaccordance with the methods as previously described herein is provided.The iron-alloy powder is admixed with substantially pure iron powder andpreferably carbon powder, in the amounts previously described herein, toform the metallurgical powder compositions of the present invention.Additionally other additives can be added to the metallurgical powdercomposition in the amounts previously described herein. For example, anycombination of alloying powders, lubricants, binding agents, machiningagents, plasticizers, or any other conventional metallurgical powderadditive may be added.

[0052] The method of combining the iron-alloy powder, the substantiallypure iron powder, the carbon powder, and other desired additives may beperformed according to any technique well known to those skilled in theart. Preferably, the method used results in a uniformly mixedmetallurgical powder composition that does not readily segregate.Moreover, the order of addition of the iron-alloy powder, thesubstantially pure iron powder, the carbon powder, and other desiredadditives is not critical. Preferably, however the order of addition isin a manner to achieve a uniform mixture of the metallurgical powdercomposition.

[0053] In a preferred embodiment, the methods of the present inventioninclude adding a binding agent to the metallurgical powder compositionto bond the iron-alloy powder, the substantially pure iron powder andother additives to inhibit segregation. The binding agent can be addedto the powder mixture according to any technique known to those skilledin the art. For example, the procedures taught by U.S. Pat. Nos.4,834,800 to Semel; 4,483,905 to Engstrom; 5,154,881 to Rutz et al.; and5,298,055 to Semel et al.; and WO 99/20689, published Apr. 29, 1999, canbe used, the disclosures of which are hereby incorporated by referencein their entireties. Preferably, the binding agent is added in a liquidform and mixed with the powders until good wetting of the powders isattained. Those binding agents that are in liquid form at ambientconditions can be added to the powder as such, but it is preferred thatthe binding agent, whether liquid or solid, be dissolved or dispersed inan organic solvent and added as a liquid solution, thereby providingsubstantially homogeneous distribution of the binding agent throughoutthe mixture. The wet powder is thereafter processed using conventionaltechniques to remove the solvent. Typically, if the mixes are small,generally 5 lbs. or less, the wet powder is spread over a shallow trayand allowed to dry in air. On the other hand, in the case of largermixes, the drying step can be accomplished in the mixing vessel byemploying heat and vacuum.

[0054] Also, the sequence of addition of the binding agent and alubricant, if desired, can be varied to alter the final characteristicsof the metallurgical powder composition. For example, the procedurestaught in U.S. Pat. No. 5,256,185 to Semel et al., which is herebyincorporated by reference in its entirety, can be used. Also forexample, the lubricant can be blended with the iron-alloy powder, thesubstantially pure iron powder, the carbon powder, the alloying powdersand other optional additives, and then, subsequently, the binding agentis applied to that composition. In another method, a portion of thelubricant, preferably from about 50 to about 99 weight percent, morepreferably from about 75 to about 95 weight percent, is added to amixture of the iron-alloy powder, the substantially pure iron powder,and other additives, then the binding agent is added, followed byremoval of the solvent, and subsequently the rest of the lubricant isadded to the metal powder composition. One further method is to add thebinding agent first to a mixture of the iron-alloy powder and otheradditives, remove the solvent, and subsequently add the entire amount ofthe lubricant.

[0055] The metallurgical powder compositions of the present inventionthus formed can be compacted in a die according to standardmetallurgical techniques to form metal parts. Typical compactionpressures range between about 5 and 200 tons per square inch (tsi)(69-2760 MPa), preferably from about 20-100 tsi (276-1379 MPa), and morepreferably from about 25-60 tsi (345-828 MPa).

[0056] Following compaction, the part can be sintered, according tostandard metallurgical techniques at temperatures, sintering times, andother conditions appropriate to the metallurgical powder composition.For example, in a preferred embodiment, sintering temperatures rangefrom about 1900° F. to about 2400° F. and are conducted for a timesufficient to achieve metallurgical bonding and alloying. Themetallurgical powder composition may also be double pressed and doublesintered by techniques well known to those skilled in the art.

[0057] Metal parts of various shapes and for various uses may be formedfrom the metallurgical powder compositions of the present invention. Forexample, the metal parts may be shaped for use in the automotive,aerospace, or nuclear energy industries.

[0058] It has been found that the metallurgical powder compositions madein accordance with the methods of the present invention haveunexpectedly superior machinability properties. These improvements areespecially observed when the metallurgical powder composition containsfrom about 10 weight percent to about 30 weight percent of aniron-molybdenum prealloy powder, from about 70 weight percent to about90 weight percent of a substantially pure iron powder, from about 0.1weight percent to about 3.0 weight percent of a carbon powder, and fromabout 0.1 weight percent to about 3.0 weight percent of a coppercontaining powder. Preferably, the iron molybdenum prealloy containsfrom about 0.40 to about 2.0 weight percent molybdenum and from about 98weight percent to about 99.6 weight percent iron. The machinability canbe further enhanced through the presence of a machining agent such asmanganese sulfide in the metallurgical powder composition.

EXAMPLES

[0059] Some embodiments of the present invention will now be describedin detail in the following Examples. Iron-based metallurgical powdercompositions were prepared in accordance with the methods of the presentinvention. Comparative metal powder compositions were also prepared. Thepowder compositions prepared were compacted and sintered to form metalparts and evaluated for machinability.

Comparative Examples 1 to 2 and Examples 3 to 10

[0060] Metallurgical powder compositions having the compositions shownin Table 1 were prepared. TABLE 1 Composition of Metal Powders Tested FeFe-Alloy Carbon Cu MnS Lubricant Examples Powder Powder, wt % wt % wt %wt % wt % Control Balance 0.0 0.5 2.0 0.0 0.0 Comp. Ex. Balance 0.0 0.61.75 0.0 0.75 1 Comp. Ex. Balance 0.0 0.6 1.75 0.35 0.75 2 Example 3Balance 10.0 0.6 2.0 0.35 0.75 Example 4 Balance 15.0 0.6 2.0 0.35 0.75Example 5 Balance 20.0 0.6 1.75 0.35 0.75 Example 6 Balance 20.0 0.6 2.00.35 0.75 Example 7 Balance 25.0 0.6 2.0 0.35 0.75 Example 8 Balance30.0 0.6 2.0 0.35 0.75 Example 9 Balance 35.0 0.6 2.0 0.35 0.75 ExampleBalance 40.0 0.6 2.0 0.35 0.75 10

[0061] The compositions were prepared by uniformly blending all theingredients in the amounts shown in Table 1. The iron powder used in allexamples was Ancorsteel 1000A available from Hoeganaes Corporation,located in Cinnaminson, N.J. The iron-alloy powder used in all exampleswas Ancorsteel™ 85HP steel powder also available from HoeganaesCorporation. Ancorsteel 85HP is an iron-molybdenum prealloy powdercontaining about 0.85 weight percent molybdenum. The graphite used inall examples (shown as “Carbon” in Table 1) had a weight averageparticle size of about 6 to 8 microns and was obtained from AsburyGraphite Mills, Inc., located in Asbury, N.J. The copper powder (shownas “Cu” in Table 1) used in all examples was Accupowder from AccupowderCorporation. The copper powder had a weight average particle size offrom about 10 microns to about 14 microns and a purity of 99.5 weightpercent. The “MnS” shown in Table 1 is manganese sulfide, a machiningagent. The lubricant shown in Table 1 was Acrawax™ C lubricant. AcrawaxC is a synthetic wax and was obtained from Algroup Lonza located in FairLawn, N.J.

Example 11

[0062] The metal powder compositions of Comparative Examples 1 to 2 andExamples 3 to 10 were evaluated for machinability.

[0063] To evaluate machinability, each of the metallurgical powdercompositions in Table 1 were compacted into 4 inch diameter by 1 inchthick discs having a density of 6.8 g/cm³. The discs were sintered at2050° F. for 30 minutes in an atmosphere of 10% hydrogen and 90%nitrogen and allowed to cool to ambient temperature.

[0064] Prior to conducting the machinability tests, each drill bit wascalibrated in the following manner. Twenty drill bits of 0.25 inchdiameter were used to drill 0.95 inch deep holes in discs formed fromthe “Control” powder shown in Table 1. Each drill bit was used to drillapproximately 2 to 3 holes for a total of about 40 to about 60 holes.The holes were drilled at a feed rate of 0.005 inches per revolution anda cutting speed of 2220 rpm. During drilling the drill torque and drillthrust were measured automatically for each drill bit, and an averagedrill torque and thrust were calculated from all measurements. Onlydrill bits having a drill torque and thrust within ±5 percent of theaverage were used in the machinability tests.

[0065] Using the same equipment used to calibrate the drill bits, discsformed from each of the metallurgical powder compositions shown in Table1 were drilled with holes having a depth of 0.95 inches until the drillbit failed (e.g., wear exceeds a predetermined level). For each holedrilled, a feed rate of 0.005 inches per revolution and a cutting speedof 2220 rpm was used. The drill torque and drill thrust were measuredthroughout the test, and wear measurements on the drill bit were takenevery ten holes drilled. The wear measurements were taken by aMicrodynascope Model 5E Universal Inspection and Gauging System,supplied by Vision Engineering, located in Surrey, England. Table 2shows the results of the machinability testing. The mean thrust was themean value of thrust for all holes drilled prior to failure of the drillbit. Table 2 also shows the number of holes drilled to failure that wasused for calculating the mean thrust. The number of holes drilled tofailure depended in part on the strength of the material (increasing thestrength decreases the number of holes to failure). TABLE 2Machinability Results Composition Wt % of Number of Holes Mean Thrust,of Disc Prelloy Powder Drilled to Failure (lbs) Comp. Ex. 1 0.0 95 273.0Comp. Ex. 2 0.0 775 210.6 Example 3 10.0 34 161.6 Example 4 15.0 622166.0 Example 5 20.0 838 167.2 Example 6 20.0 398 195.5 Example 7 25.0550 223.3 Example 8 30.0 383 140.7 Example 9 35.0 435 129.5 Example 1040.0 476 131.0

[0066] The results in Table 2 show that the addition of the iron-alloypowder in an metallurgical powder composition reduces the mean thrust ofa drill bit during the drilling of a disc. For example, although themean thrust can be reduced somewhat by the addition of manganese sulfideto an iron based powder composition (see comparative Example 1 incomparison to Comparative Example 2), further improvement can beachieved by addition of a iron-alloy powder. The results for mean thrustobtained for Comparative Examples 1 to 2 and Example 5 are shown inFIG. 1. FIG. 1 is a bar graph showing mean thrust for discs preparedfrom Comparative Examples 1 to 2 and Example 5. By reducing the meanthrust, there is less wear on the drill bit leading to such benefits asincreased lifetime of the drill bit.

[0067] There have thus been described certain preferred embodiments ofthe improved metallurgical powder compositions of the present invention,and methods of making and using the same. While preferred embodimentshave been disclosed and described, it will be recognized by those withskill in the art that variations and modifications are within the truespirit and scope of the invention. The appended claims are intended tocover all such variations and modifications.

What is claimed is:
 1. A method of making a metallurgical powdercomposition comprising the steps of: (a) providing an iron-alloy powdercomprising iron and at least one alloying additive, wherein the alloyingadditive is present in an amount of from about 0.01 weight percent toabout 7 weight percent and the iron is present in an amount of at least85 weight percent based on the total weight of the iron-alloy powder;and (b) admixing with the iron-alloy powder a substantially pure ironpowder and carbon to form a metallurgical powder composition, whereinthe metallurgical powder composition comprises from about 5 weightpercent to about 40 weight percent of the iron-alloy powder, at least 55percent by weight of the substantially pure iron powder, and at least0.1 weight percent of the carbon based on the total weight of themetallurgical powder composition.
 2. The method of claim 1 wherein thealloying additive in the iron-alloy powder is selected from the groupconsisting of molybdenum, chromium, vanadium, tungsten, and combinationsthereof.
 3. The method of claim 2 wherein the alloying additive ismolybdenum.
 4. The method of claim 3 wherein the molybdenum is presentin the iron-alloy powder in an amount of from about 0.1 to about 2.0weight percent, based on the total weight of the iron-alloy powder. 5.The method of claim 1 wherein the metallurgical powder compositionfurther comprises at least one alloying powder.
 6. The method of claim 5wherein the alloying powder comprises copper, nickel, or combinationsthereof.
 7. The method of claim 1 wherein the metallurgical powdercomposition further comprises copper, nickel, graphite, manganesesulfide, or combinations thereof.
 8. The method of claim 1 wherein themetallurgical powder composition comprises from about 10 weight percentto about 30 weight percent of the iron-alloy powder based on the totalweight of the metallurgical powder composition and wherein theiron-alloy powder comprises from about 0.1 weight percent to about 2weight percent molybdenum based on the total weight of the iron-alloypowder.
 9. The method of claim 8 wherein the metallurgical powdercomposition comprises from about 70 weight percent to about 95 weightpercent of the substantially pure iron powder, from about 0.1 weightpercent to about 3 weight percent carbon, and from about 0.10 to about3.0 weight percent copper, based on the total weight of themetallurgical powder composition.
 10. An improved metallurgical powdercomposition comprising: (a) from about 5 weight percent to about 40weight percent of an iron-molybdenum alloy powder comprising iron andmolybdenum, wherein the amount of molybdenum is from about 0.10 weightpercent to about 7.0 weight percent and the amount of iron is at least85 weight percent based on the weight of the iron-molybdenum alloypowder; (b) at least 55 weight percent of a substantially pure ironpowder; and (c) from about 0.1 weight percent to about 3 weight percentof carbon.
 11. The metallurgical powder composition of claim 10 whereinthe metallurgical composition further comprises at least one alloyingpowder.
 12. The metallurgical powder composition of claim 10 wherein themetallurgical composition further comprises nickel, copper, graphite,manganese sulfide, or combinations thereof.
 13. The metallurgical powdercomposition of claim 10 wherein the metallurgical powder compositioncomprises from about 10 weight percent to about 30 weight percent of theiron-molybdenum alloy powder, from about 70 weight percent to about 95weight percent of the substantially pure iron, from about 0.1 weightpercent to about 2 weight percent of the carbon, and from about 0.10 toabout 3.0 weight percent copper, based on the total weight of themetallurgical powder composition.
 14. A method of forming a metal partcomprising the steps of: (a) providing a metallurgical powdercomposition comprising a mixture of: (i) from about 5 weight percent toabout 40 weight percent, based on the weight of the metallurgical powdercomposition, of a iron-alloy powder comprising iron and at least onealloying additive, wherein the alloying additive is present in an amountof from about 0.01 weight percent to about 7 weight percent and the ironis present in an amount of at least 85 weight percent, based on thetotal weight of the iron-alloy powder; (ii) at least 55 weight percentof substantially pure iron powder; and (iii) at least about 0.1 weightpercent of carbon; and (b) compacting the metallurgical powdercomposition at a pressure of at least about 5 tsi to form a metal part.15. The method of claim 14 wherein the alloying additive is molybdenumand is present in the iron-alloy powder in an amount of from about 0.1to about 3.0 weight percent, based on the total weight of the iron-alloypowder.
 16. The method of claim 15 further comprising the step ofsintering the compacted metal part at a temperature of at least 1900° F.to form a machinable metal sintered part.